Comparison of n-alkane molecular, carbon and hydrogen isotope compositions of different types of plants in the Dajiuhu peatland, central China

Abstract

Long chain n-alkanes preserved in peat deposits have been widely used to reconstruct paleoenvironmental and paleoecological changes. However, our knowledge of how the leaf wax molecular and isotopic compositions of peat sequences might respond to changes in plant communities is limited. This study investigates the n-alkane molecular, carbon and hydrogen isotopic compositions of plant species collected from the Dajiuhu peatland, central China. The results show that forb and graminoid plants growing in peatlands have a relatively higher carbon preference index of long-chain n-alkanes than shrubs, ferns and aquatic plants. The δ13C values of individual n-alkanes generally decrease with increasing chain lengths, and different plant groups have similar δ13C values of C31 and C33n-alkanes. An exception is Sphagnum, which has more negative δ13C values of C23 and C25 than those of its longer chain length homologues. Relative to peat pore water δD values in different seasons and different peat depths, the Dajiuhu plants normally exhibit relatively large hydrogen isotope fractionations, and the fractionations gradually increase from graminoid to forb to shrub. Taken together, these results highlight the influence of different kinds of vegetation on the collective molecular and isotopic ratios of n-alkanes in peat deposits.